Identifying the Main Sewer Clean-Out in Your House

Sewer clean out surrounded with grass near pavement

The Spruce / Adelyn Duchala

A drain clog in an individual plumbing fixture, such as a tub or sink, is one thing—it's a problem that is usually fairly easy to fix. But it is another matter entirely when you have a main drain line stoppage—a clog in the large, main drain line that serves your entire house and delivers all wastewater to the civic sewer system or to a septic drain field. When a main drain clog happens, raw sewage no longer flows as it is supposed to, and it can back up into your entire house with results that can be disastrous. Until the clog is removed no drains in any of your plumbing fixtures can be safely used. It is an unpleasant and potentially very expensive problem. 

The Main Clean-Out

Clearing a main sewer line stoppage is best approached from a fitting known as the main clean-out or main house trap. Every house should have one, although unfortunately, some houses don't. It is the best place for you or a plumber to use a drain snake or motorized auger to dislodge the clog in the main drain line and return your house's drain system to proper function. 

Finding the main clean-out isn't always easy, though. Its location within a home will vary depending on the house style and the geographic climate where you live. Here are some tips for locating your main drain. 

Outdoor Clean-Outs

In warm climates where homes are built on slab foundations, the main clean-out fitting is often outside, usually near the exterior walls of the home. Look behind bushes, or in a metal or plastic box recessed into the ground. The main clean-out fitting is usually a large-diameter pipe with one or two threaded plugs in the top. It may be extending above the ground near an outside wall or may be contained inside a ground box covered by a metal cover. 

In a Bathroom or Utility Area

In other homes with slab foundations, the main drain may be located in a bathroom, usually on the floor near the toilet, or in a garage or utility area, usually near a floor drain. In these locations, the threaded plug may be flush-mounted into the floor or may be threaded into a short length of large-diameter pipe extending up from the floor. It can be opened with a large pipe wrench in order to provide access for drain-clearing tools. These plugs, if not removed for long periods of time, may not unscrew. In this case, they may have to be chopped out by hammer and chisel and replaced with a fit-all plug. This is a universal plug with a lead ring that is hammered on to make a seal.

In a Basement

Finally, in houses in colder climates where the standard construction practice is to build homes over basements, the main clean-out is usually found on the basement floor, usually near the foundation wall. A threaded plug will fit into a short length of large-diameter pipe that extends up from the floor. If you have trouble finding the clean-out, follow a direct line from the vertical soil stack to the foundation wall, following the shortest path—the main clean-out will likely be located along this line. If not this kind of fitting, there may be a Y-fitting at the bottom of the main drain soil stack where it disappears under the concrete slab.

In larger homes, there may be two or even three clean-out fittings, one for each of the main drain pipes running from separate soil stacks out to the street.

Routine Maintenance

Main drain line cleaning can be done by most plumbers, but there are also companies specializing in this work. An annual inspection and cleaning by a sewer specialist is a good idea, especially if you have a landscape with large trees. Tree roots can easily penetrate sewer lines, and a regular routine of sewer drain line cleaning may prevent a disastrous blockage.

Cleaning the main drain blockage can be done by a homeowner, but it may require special tools, such as a motorized drain auger available for rental at tool centers and major home improvement stores.